It's like in-band signalling in the telephone network, where if you whistled the right tones into your call, you could affect the way the network processed said call. Except Ma Bell responded to that system being exploited by designing a comprehensive overhaul of the way signalling was handled, and spent a squadzillion dollars upgrading millions of tons of switching equipment to categorically exclude that entire class of attack from ever being possible.
Software, on the other hand, would need to replace no equipment whatsoever. Existing processors are perfectly capable of running code that handles the length of a string separately from its contents. There are existing languages that do this, they're just.... not used. String escapes and buffer overflows exist, going on decades now, due to nothing more than laziness, inertia, and negligence.